This application claims the benefit of priority under 35 U.S.C. xc2xa7 119 to Japanese Patent Application No. 241993/2001, filed on Aug. 9, 2001, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a power transmission mechanism for use in a toy vehicle with an engine. More particularly, the present invention relates to a mechanism for realizing a smooth shift between forward and reverse operations of a toy vehicle with an engine by radio control.
In order to allow a toy vehicle equipped with an engine to perform reverse running in addition to forward running, it is necessary to solve the problem of the heavy load applied to the rotation transmission mechanism when the clutch is engaged instantaneously during switching between forward rotation and reverse rotation.
To solve the above-described problem, Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 9-285649 proposes a structure in which a forward gear and a reverse gear, which rotate in opposite directions to each other, are disposed at both sides of a clutch plate. Each gear has a circumferential groove and an engaging member fitting hole formed on the front side thereof. The engaging member fitting hole intersects the groove at right angles. A metallic engaging member is fitted in the engaging member fitting hole. With this structure, however, it is difficult to provide a braking function. If a braking function is provided, the structure is expected to become extremely complicated because it is necessary to construct a brake mechanism that operates for each of the forward and reverse gears.
Another structure that allows reverse running in addition to forward running is disclosed in Japanese Patent Post-Exam Publication No. Hei 5-70479. The structure has two clutch mechanisms for transmitting rotational force of an engine to a rotational driving shaft through gears. A rotary disk of one clutch mechanism is held with a brake member, and a brake member for a rotary disk of the other clutch mechanism is opened to allow the rotary disk to rotate, thereby enabling the rotational driving shaft to be rotated either forwardly or reversely. However, this method requires a complicated structure and is hence likely to suffer increased costs.
Accordingly, an object of the present invention is to provide a power transmission mechanism for use in a toy vehicle with an engine that realizes a smooth shift between a forward operation and a reverse operation with a relatively simple structure.
To attain the above-described object, the present invention provides a power transmission mechanism for use in a toy vehicle with an engine. The power transmission mechanism includes an input shaft capable of transmitting rotational driving force from an engine, and an output shaft capable of transmitting the rotational driving force to a driving wheel of the toy vehicle. A first gear is secured to the input shaft. A second gear connectable to the input shaft through a clutch mechanism is provided around the input shaft through a one-way clutch that allows the input shaft to rotate freely in the direction of rotation of the driving force from the engine when the clutch mechanism is in a disengaged state but does not permit rotation of the second gear relative to the input shaft in a direction opposite to the direction of rotation of the driving force from the engine. A brake mechanism is provided to restrain the rotation of the second gear. A third gear is provided around the output shaft. The third gear is in mesh with the first gear. A fourth gear is provided around the output shaft. The fourth gear is in mesh with the second gear. A first bevel gear is secured to the output shaft. A second bevel gear is provided on the output shaft in a free state to face the first bevel gear. The second bevel gear is secured to the third gear. A third bevel gear is provided at a fixed position with respect to the fourth gear. The third bevel gear is in mesh with both the first bevel gear and the second bevel gear. The gear ratio between the first gear and the third gear is equal to the gear ratio between the second gear and the fourth gear.
In the forward mode of the present invention, as the input shaft rotates, the first gear rotates, thereby driving the third gear to rotate. The rotation of the input shaft causes the clutch mechanism to be engaged. Consequently, the second gear rotates, thereby driving the fourth gear to rotate. Because the gear ratio between the first gear and the third gear is the same as that between the second gear and the fourth gear, the third gear and the fourth gear rotate synchronously, and the output shaft is driven so that the wheels rotate in the forward direction.
In the reverse mode, the clutch mechanism is disengaged, and the brake of the brake mechanism is activated. Because the clutch mechanism has been disengaged, the second gear and the fourth gear, which is in mesh with the second gear, are not driven. The third gear driven by the rotation of the first gear drives the output shaft to rotate in a direction opposite to the direction in the forward mode through the first to third bevel gears so that the wheels rotate in the reverse direction.
In the brake mode, the clutch mechanism is disengaged, and the brake of the brake mechanism is activated as in the case of the reverse mode. Although the rotation of the wheels causes the output shaft to rotate, because the fourth gear is placed stationary, the third gear is caused to rotate in a direction opposite to the direction of rotation of the output shaft through the first to third bevel gears. Consequently, the input shaft is urged to rotate in the locking direction of the one-way bearing through the first gear. However, because the rotation of the second gear is restrained by the brake mechanism, the rotation of the third gear performs the function of braking the output shaft, i.e. the wheels.
Thus, the present invention allows a toy vehicle with an engine to perform reverse running with a relatively simple structure by employing bevel gears as stated above. It also becomes possible to apply the brakes.
Preferably, the clutch mechanism in the above-described power transmission mechanism is engaged when a user actuates a throttle trigger for operating the toy vehicle to establish a forward mode, and disengaged when the user actuates the throttle trigger to establish a reverse mode. Thus, the present invention allows the clutch mechanism to be engaged and disengaged simply by operating the throttle trigger in each mode.
Preferably, the brake mechanism in the power transmission mechanism does not perform a braking operation when the user actuates the throttle trigger to establish the forward mode, but activates a braking operation when the user actuates the throttle trigger to establish the reverse mode. Thus, the present invention allows the brake mechanism to be activated and released simply by operating the throttle trigger in each mode.
Preferably, the above-described clutch mechanism includes a clutch housing. A plurality of clutch shoes are accommodated in the clutch housing so that when the clutch shoes move outward, the outer peripheral surfaces thereof are capable of coming in frictional contact with the inner surface of the clutch housing. The clutch shoes each have a claw extending in the axial direction of the input shaft. A clutch cam is secured to the input shaft to lie between the clutch shoes. The clutch cam is adapted to move the clutch shoes so that the outer peripheral surfaces thereof come in frictional contact with the inner surface of the clutch housing by a cam action in response to the rotation of the input shaft. The clutch mechanism further includes a shift ring having claw restraining grooves corresponding in number to the claws. The shift ring is movable between a first position at which the claws are released from the claw restraining grooves to allow the clutch shoes to come in frictional contact with the inner surface of the clutch housing and a second position at which the claws are received in the claw restraining grooves to restrain the clutch shoes from moving so as to come in frictional contact with the inner surface of the clutch housing. When the user actuates the throttle trigger to establish the forward mode, the shift ring moves to the first position, whereas when the user actuates the throttle trigger to establish the reverse mode, the shift ring moves to the second position.
According to the present invention, simply actuating the throttle trigger causes the shift ring to move in the axial direction of the input shaft, thereby making it possible to restrain the clutch shoes from coming in frictional contact with the inner surface of the clutch housing and to release the clutch shoes from the restraint.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof, taken in conjunction with the accompanying drawings.